Conventionally, magnetrons have been known as instruments for generating microwaves, which are used for radar devices, microwave ovens, etc. In order to appropriately operate the magnetron, it is necessary to raise the temperature of a cathode of the magnetron to a certain temperature or above. If the cathode temperature of the magnetron is too low, the cathode may be damaged and, thus, the life of the magnetron may be shortened. For this reason, it is generally known that a heater is provided near the cathode and the cathode is preheated by applying current to the heater.
Since the magnetron cannot be used during the preheating, a device such as the radar device cannot be operated. Moreover, in order to certainly prevent from operating the magnetron while the temperature of the cathode is low, the preheating time length is set long enough in many cases. Therefore, a long waiting time is needed after turning on the device such as the radar device before making it into the ready-to-use state. JP3,199,909 and JP06-342058A disclose radar devices which can shorten the waiting time to some extent.
The radar device of JP3,199,909 is provided with a positioning device such as a GPS receiver, and is configured to acquire latitude and longitude information and date information from the positioning device. The radar device estimates a temperature around a ship concerned (which equips the radar device) based on the information and the past meteorological data. The preheating time of the magnetron is set shorter as the estimated temperature becomes higher (i.e., at a lower latitude or during summer) and, on the other hand, the preheating time is set longer as the estimated temperature becomes lower (i.e., at a higher latitude or during winter). Thereby, a suitable preheating time is set according to the ambient temperature to shorten the waiting time.
The radar device of JP06-342058A is provided with a temperature detector, and is configured to measure the temperature around the ship concerned. This radar device shortens the waiting time by setting the preheating time of the magnetron based on the ambient temperature.
However, the radar device disclosed in JP3,199,909 needs to be provided with the GPS receiver or the like, and, further needs to be connected with the GPS receiver. Therefore, the preheating time cannot be shortened by this radar device alone. Moreover, even if the radar device estimates the temperature based on the meteorological data, there is variation in climate, and since the preheating time has to have some margin taking the variation into consideration, the preheating time will become inevitably longer.
Meanwhile, since the radar device disclosed in JP06-342058A needs to be provided with the temperature detector, it will be high in cost. Moreover, since the preheating time of the magnetron involves not only the ambient temperature but the internal temperature of the radar device, the condition of the heater and the like, it is difficult to estimate the preheating time correctly. For these reasons, the preheating time will be inevitably longer to some extent, which is redundant, similar to the case of JP3,199,909.